Method of making composite articles



United States Patent 0 3 194 656 METHSD (1 F MAKII IG CQWUSlTE ARTiCLlEMilton B. Vordahl, Beaver, P2,, assignor to Crucible Steel Company ofAmerica, Pittsburgh, lPa., a corporation of New Jersey No Drawing. FiledAug. 10, 15 61, Ser. No. 136,495 8 tilaims. (ill. 7S--l35} Thisinvention relates to a method of making finegrained, hard alloysutilizing the principles of soliquidus (solidus-liquidus) componentinterchange, and to a method of making shaped articles thereof.

In the prior art practice of making alloys hardened by high meltingpoint compounds, the usual procedure involves the steps of melting allof the constituents in an induction furnace, heating to the top side,i.e., a temperature sufficiently high to melt all of said constituents(usually over 4000 F.), and thereafter casting. The resultant castingsof this procedure are characterized, in the main, by a very coarsedendritic distribution and the segregated condition of the cast materialis such that a tremendous amount of working is required before anydegree of structural homogeneity is obtained which permits substantiallyuniform physical properties. As indicated heretofore, the ultimatemelting temperature of alloying constituents is quite high, from whichfact it necessarily follows that requirements for materials ofconstruction, e.g., furnace linings, crucibles, molds, etc., are veryrigid and constitute a distinct disadvantage. In addition, themanufacture of hard alloy shapes by prior art methods is attended by thefurther disadvantage of high capital investment. As an illustrativeexample of the prior art, consider an attempt to prepare a nickel basealloy containing an appreciable volume fraction or" TiB In such case,the temperature range between the melting point of the matrix metal,i.e., nickel, and the melting point of the compound, i.e., TiB isgreater than 1000 F. and constitutes a soliquidus spread of suchmagnitude that density differences and cooling rate practicalities arevirtually prohibitive of the obtention of a final alloy having asubstantially distributed, high volume fraction of said compound.

Accordingly, a principal object of the present invention is to providean improved method of making alloys containing high melting pointcompounds which method is unattended by the foregoing disadvantages ofthe prior art.

Another object of the invention is to provide a method of makingsubstantially segregation-free alloys comprising a ductile matrixcontaining a high volume fraction of hard melting-point compounds.

A further object of the invention is to provide a method of makingshaped articles of substantially segregationfree alloys hardened byrefractory compounds, which articles are not readily made by othermethods.

Other objects of the invention will be apparent from the followingdescription.

In general, the method of the invention contemplates the preparation offine grained, hard alloys comprising a matrix metal and a high volumefraction of a high melting point compound by mixing two or moreingredients, the resultant admixture containing all of the essentialcomponents of said high melting point compound and the individualcompositions of said ingredients being so formulated that eachingredient contains no more than a relatively small amount of all ofsaid components and at least one of said ingredients has a liquidustemperature which is far below that of said high melting point compoundand substantially below that of said matrix metal. This latterrequirement is important in the sense that as the liquidus temperatureof the most refractory phase ice of the starting ingredients approachesthe liquidus temperature of the most refractory phase of the finalalloy, the advantage of the method vanishes. To accrue the principaladvantages of the inventive method, the liquidus temperatures of thosestarting ingredients which are melted during the practice of said methodshould be sufiiciently low to simplify materials of constructionproblems, such as those associated with choice of crucible materials,and the temperature at which the sought high melting point compoundforms should be sufficiently lower than the melting point thereof as toconstitute effectively a substantial super-cooling. In this latterconnection, what is meant is that the high melting point compound shouldform at a temperature below the melting point of the compound and atleast one of the components thereof should derive from a material in theliquid state. Ordinarily, formation of a solid high melting pointcompound at a temperature lower than its melting point would beaccomplished by super-cooling the molten compound. In such case thedifference between the melting point and the temperature at which thesolid compound actually forms is the measure of super-cooling. Inaccordance with the practice of the instant invention, for the samesystem, the measure of super-cooling is the same. However, beyond thisfeature similarities cease to exist. Obviously, the prior art methodnecessitates initially attaining a temperature above the melting pointof the high melting point compound, whereas the inventive method doesnot. A major disadvantage of the prior art method is its lack ofeffective control over compound coarsening and distribution. This resultaccrues from cooling of the molten mass which forms phases in the orderof decreasing refractoriness, thus permitting the growth of morerefractory phases to trap lesser refractory phases resulting indendritic segregation. On the other hand, the inventive method exhibitsgreater control over the size and distribution of high melting pointcompounds within the matrix metal since such compounds form only at theexpense of the low melting starting mixture, i.e., the components ofsaid compounds are necessarily extracted from said mixture, the liquidustemperature of which is thereby raised. Ensuing solidification of themixture effectively holds the high melting point compounds at formationsites and segregation is thus minimized or obviated entirely.

In accordance with the inventive concept, soliquidus componentinterchange may take place between starting ingredients while each ispresent only as a liquid phase or While one is present as a liquid phaseand another is present as a solid phase. Exemplary of the former case isthe mixing of molten starting ingredients or the mixing of solidstarting ingredients having the same or approximately the same meltingpoints, followed by heating to effect melting of all of saidingredients. Exemplary of the latter case is the mixing of solidstarting ingredients having dissimilar melting points, followed byheating to effect melting of the lower melting ingredient. In thislatter case it is, of course, necessary that the higher meltingingredients be finely divided or powdered in order that a maximumsurface area be available to promote component interchange between theliquid and solid phases. An inherent advantage of the invention accruesfrom the fact that this requirement is unnecessary where an ingredientundergoes melting, in which case granular or even lump material may beemployed.

The invention also contemplates soliquidus component interchangereactions involving both liquid-liquid and liquid-solid reactions,either consecutively or simultaneously during the course of theformation of a desired final alloy. Thus, it will be seen that theinvention requires the provision, in each contemplated system, of atarea-,eee

least one starting ingredient having a melting point ape preciably lowerthan that of the lower melting material,

i.e., the matrix metal, of the desired final alloy. For this purpose,certain low melting point compositions are 4 occur in ,situ or uponcasting into any desired form andresults in a fine-grained structure incontrast to the coarsegrained structure obtained by following the topside temperature practice of the prior art.

useful, e.g., eutectic or near-eutectic compositions. Where theprinciples of soliquidus component interlllustrative of alloys producedin accordance with the change are to be applied by wayof reheating alowmeltpresent invention, together with the low meltingstarting startingmixture of alloys 1n SOllCl form, it is ading mixtures therefor, are theexamples given below in vantageous in certain mstances to add part oreven all Table I: of one or some of the essential components of the highTable 1 Low melting starting mixture Final alloy High melting Alloy 1Alloy 2 Matrix point compound Ni+B Nl+Ti Ni Tm, Ni+Go+B Ni+Ti+(Fe, W,Mo, Ob, Cr) Ni-I-Co-i-(Fe, W, Mo, ob,-or); Th3, Ni+Fe+C Ni-t-Fe-l-Ti i eT C i+8o+Fe+G lgliili-i-(Fe, W, Mo, Cb, Cr)- Ni+Co+Fe+(W,Mo,(moi)--- e+e 1 e 1 Fe+Ni+Co+C Fe|-Ti+(Ni,Co,Or,M0) Fe+Ni+Co+(Cr,Mo) TiC Co+O. Co+TiOo 'IiC Go+B- Co+Ti 00.- TlBg Cu+B Ou-l-li 011-. T Bz Cu-l-Si Cu+Ti CuT1581: Cu+B Cu+Zr Ou ZIB: Ni+B Ni+Zr Ni ZrB;

' Norm-In general, Zr and Hi can be substituted wherever Ti appears inTable I.

In the case of the examples listed in Table L'the selectionof Alloy 2 isbased essentially upon the existence of {a low melting point eutecticcomprising'a potent compound former, e.g., Ti, and a useful matrixmetal, e.g., Ni. Alloy 1 is selected with the thought in mind ofproviding a sufficient amount of a particular non-metal, e.g., B, whichwill combine with the compound former of Alloy 2 to provide a highvolume fraction of a high melting point compound. To secure the chiefadvantages of the invention, such a compound should exhibit a minimumsuper-cooling effect of about 400 C. While all of the Alloy 1 examplesof Table I are denoted as alloys of. the matrix metal and the non-metalcomponent of the high melting pointcompound, e.g., Ni-i-B (Ni containingB either in solid solution or as a dissociable compound), nevertheless,it is'within the scope of the invention to provide the non-metal inelemental form either in place of Alloy 1 or as a separate additionthereto.

Although the principles of the inventive method as applied to the mixingof liquids require essentially that no one of the low melting startingmixture alloys should contain all of the essentialcomponents of the highmelting point compound of the final alloy, a small admixture may in somecases be desirable for the purpose of altering characteristic of a meltor for adding more of a component than a single melt can hold within thetemperature requirements. 7 In any case, the bulk, e.g., over-60%, ofthe high melting point compound must be formed in situ after mixingmelts of the starting alloys in order to realize the full advantages ofthe invention.

Asindicated heretofore, the mixing of more than two melts is within thescope of the present invention. In such case, however, the justificationfor any additional advantage to be gained thereby should be weighedagainst the additional complication of necessarily mixing a number ofmelts simultaneously and with great rapidity.

Exemplary of the aspect of the invention involving principally.liquid-liquid reaction is the procedure of preparing two melts, the onea eutectic composition of Ni-i-B,

melting point less than about 2000 F., the other eutectic melting pointcompound as a separately prepared powder. This may greatly simplifycomminution of said components or permit additions thereof in quantitiesconsiderably beyond solubility limits.

The liquid-solid reaction aspect of the invention may be illustrated byapplication thereof to melts of Ni-l-B and Ni+Ti which, asaforementioned, are amenable also to the liquid-liquid reactionprocedure. In this case the two melts are separately solidified andgranulated (fine powders not being necessary or desirable), mixed, andheated to a temperature slightly higher than the melting point of thelower melting component, i.e., Ni-l-B. Immediately thereafter, pressureis applied to the heated mix, e.g., by spinning the mold or forcing themixthrough orifices into -a multiplicity of molds. Micromixing isaccomplished by wetting and penetration '(ultrasonics may also bevaluable here), and isaided by the exo thermic reaction involved.

In another case, such as Ni hardened by a large volume fraction, e.g.,30 to of TiC, the nickel melt will hold only a small fraction of therequired carbon, and comminution of the solidification alloyis verydifficult without loss of carbon, the latter being present as graphite.Hence, rather than employing the mixing of liquids procedure thepreparation of the desired alloy preferably proceeds by the heating ofintimately mixed powders of graphite and an approximate eutecticcomposition ofNi-l-Ii, the latter. being chosen so as to have a meltingpoint no higher than aboutl200 C.

' While some or most of the Ni could be addedas Ni powder, most (atleast of the Timust be added as a low melting alloy. Otherwise, theinventive method will show little or no advantage. over prior art powdermetallurgy methods wherein the high melting compound,

in this case TiC, ispre-preparedand used as. such. To illustrate, amixture of 10 grams of finely divided graphite, 60 grams of granularTi-30% 'Ni eutecticalloy, and 80 grams of granular Ni, .upon heatingunder light pressure to about 1200" (3., results in a mush or pasty mixcomprising a matrix of Ni throughout which there isuniformly distributed50 volume percent of-TiC. For a short period of time, up toa few secondsor minutes, after reaching the eutectic melting temperature, the pastycondition of the mix remains and permits of ready plastic deformation,e.g., forcing into molds. After solidification the resultantfine-grained, hard alloy has a density which approachesthe theoretical,and soaking for the. purpose of densification is entirely unnecessary.However, several hours of soaking for the purpose of homogenization mayin some cases be desirable after removal of the alloy from the mold.This would be done at temperatures increasing with time up to withinabout a hundred centigrade degrees of the solidus temperature of thealloy.

Among the outstanding advantages flowing from the practice of thepresent invention are the following: modest requirements for materialsof construction; low to moderate gauge pressures encountered even at thehighest temperatures employed; feasibility in many instances ofutilizing granular material, e.g., about minus 100 mesh, as well asfinely powdered material, e.g., micron particle size; ability to obtaina finer and more uniform distribution of high melting point compounds ina massive piece than is possible by prior art techniques; ability tomake some compositions which cannot be made at all by prior arttechniques.

While only a restricted number of examples have been given in the abovespecification, it is understood, of course, that the present inventionis not limited thereto, since many modifications thereof may be made andthe appended claims intend to cover such modifications as fall withinthe true spirit and scope of the invention.

I claim:

1. A method of making shaped metallic articles having a fine grainedrnicrostructure and exhibiting improved hardness and comprising an alloycontaining a matrix metal and at least one high melting point compound,comprising: preparing in a form an admixture of at least two substances,the one substance consisting of a molten alloy, said alloy having amelting point lower than that of said matrix metal, and the othersubstance comprising at least one member selected from the groupconsisting of a non-metal and an alloy thereof, said substancesproviding all of the essential components of said high melting pointcompound and in such amount as to result in a substantial increase inthe melting point of the mass when reaction between components indifferent ones of said substances occurs, said substances being socomposed individually that each contains no more than a relatively smallamount of all of said components; the energy released from a chemicalreaction causing formation of said compound by chemical reaction ofcomponents in said substances being such in relation to the amounts andheat capacity of materials present as to raise the temperature of thesystem to a temperature not exceeding the melting point of the matrixmetal; and maintaining the temperature of said admixture substantiallyless than the melting point of said matrix metal until solidification ofsaid mass occurs.

2. A method of making shaped metallic articles having a fine grainedmicrostructure and exhibiting improved hardness and comprising an alloycontaining a matrix metal and at least one high melting point compound,comprising: prepan'ng an admixture of at least two sub stances, the onesubstance consisting of a molten alloy, said alloy having a meltingpoint lower than that of said matrix metal, and the other substancecomprising at least one member selected from the group consisting of anon-metal and alloy thereof, said substances providing all of theessential components of said high melting point compound and in suchamount as to result in a substantial increase in the melting point ofthe mass when reaction between components in different ones of saidsubstances occurs, said substances being so composed individually thateach contains no more than a relatively small amount of all of saidcomponents; casting said admixture into molds; the energy released froma chemical reaction causing formation of said compound by chemicalreaction of components in said substances being such in relation to theamounts and ,heat capacity of materials present as to raise thetemperature of the system to a temperature not exceeding the meltingpoint of the matrix metal; and maintaining the temperature of saidadmixture substantially less than the melting point 6 of said matrixmetal until solidification of said mass occurs.

3. A method as in claim 2 wherein the step of casting is accompanied bythe application of pressure to said admixture.

4. A method a in claim 3 wherein said application of pressure isaccomplished by spinning said molds.

5. A method as in claim 3 wherein said application of pressure isaccomplished by forcing said admixture through orifices into amultiplicity of molds.

6. A method of making fine grained, hard alloys containing a matrixmetal, M, and at least one high melting point compound, C, said methodcomprising: preparing an admixture of at least two substances, A and B,said substances having a melting point lower than that of said matrixmetal, M, and being present in such amount as to result in a substantialincrease in the melting point of the mass upon reaction betweencomponents in different ones of said substances occurs, wherein at leastone of said substances is molten and wherein A, B, M and C are selectedfrom the same grouping consisting of one of the following groupings:

Grouping A B M C 1 Ni-l-B Ni+1i Ni TiBz 2 Ni+Co+B Ni+Ti+ Ni+C0+ TiBg(Fe, W, Mo, (Fe, W, Mo, Cb, C Cb, Cr). 3 Ni+Fe+C Ni+Fe+Ti.-. Nl+Fe TiO 4Ni-l-Oo+Fe+O Ni+Ti+ Ni+Co+Fe+ TiC (Fe, W, Mo, (W, Mo, Cb, Cr). Cb, Or).Fe+C l. Fe+Ti Fe 'IiO Fe+Ni+Co+C Fe+Ti+ Fe-I-Ni+0o+ TiO (Ni, Co, (Cr,Mo). Cr,Mo) Oo-l-T O0 'liO Co+Ti 00. i TlBg Ou-l-Ti Cu TiBz C11+Ti a. CuTiasia Cu-l-Zr Cu ZrB Ni+Zr Ni. ZrB z and maintaining the temperature ofsaid admixture substantially less than the melting point of said matrixmetal, M, until solidification of said mass occurs.

7. A method of making fine grained, hard alloys containing a matrixmetal and at least one high melting point compound, said methodcomprising: preparing an admixture of at least two substances, the onesubstance consisting of a molten alloy, said alloy having a meltingpoint lower than that of said matrix metal, and the other substancecomprising a member selected from the group consisting of a non-metaland an alloy thereof, said substances providing all of the essentialcomponents of said high melting point compound and in such amount as toresult in a substantial increase in the melting point of the mass whenreaction between components in different ones of said substances occurs,said substances being so composed individually that each contains nomore than a relatively small amount of all of said components, theenergy released from a chemical reaction causing formation of saidcompound by chemical reaction of components in said substances beingsuch in relation to the amounts and heat capacity of materials presentas to raise the temperature of the system to a temperature not exceedingthe melting point of the matrix metal, said step of preparing anadmixture comprising admixing said molten alloy with said othersubstance in molten form; and maintaining the temperature of saidadmixture les than the melting point of said matrix metal untilsolidification of said mass occurs.

8. A method of making fine grained, hard alloys containing a matrixmetal in at least one high melting point compound, said methodcomprising: preparing an admixture of at least two substances, the onesubstance consisting of a molten alloy, said alloy having a meltingpoint lower than that of said matrix metal, and the other substancecomprising a member selected from a group consisting of a non-metal andan alloy thereofysaid substances providing all of the essentialcomponents of said high meltingpoint compound and in such amount as toresult in a substantial increasein the melting point of the mass whenreaction between components in different ones of said substances occurs,said substances being so composed individually that each contains nomore than a relatively small amount of all of said components, theenergy released from a chemical reaction causing formation of saidcompound by chemical reaction of components in said substance being suchin relation to the amounts and heat capacity of materials present as toraise the temperature of the system to a temperature not exceeding themelting point of the matrix metal, the step of preparing an admixturecomprising individually comminuting said substances, admixing theresultant comminuted substances, and heating the resultant admixture toa temperature slightly higher than the melting point of the lowermelting of said substances, 'said'heat-ing' being immediately followedby application of pressure to said admixture; and maintainingthe-temperature of said admixture less than the melting point ofv saidmatrix 5 metal until solidification of said massoccurs.

References Cited by the Examiner UNITED STATES PATENTS 2,656,269 10/53Dunn et a1. 75l35 2,852,366 9/58 Jenkins 75--20l' 15 DAVID L. RECK,Primary Examiner.

RAY K. WINDHAM, ROGER L. CAMPBELL,

Examiners.

1. A METHOD OF MAKING SHAPED METALLIC ARTICLES HAVING A FINE GRAINEDMICROSTRUCTURE AND EXHIBITING IMPROVED HARDNESS AND COMPRISING AN ALLOYCONTAINING A MATRIX METAL AND AT LEAST ONE HIGH MELTING POINT COMPOUND,COMPRISING: PREPARING IN A FORM AN ADMIXTURE OF AT LEAST TWO SUBSTANCES,THE ONE SUBSTANCE CONSISTING OF A MOLTEN ALLOY, SAID ALLOY HAVING AMELTING POINT LOWER THAN THAT OF SAID MATRIX METAL, AND THE OTHERSUBSTANCE COMPRISING AT LEAST ONE MEMBER SELECTED FROM THE GROUPCONSISTING OF A NON-METAL AND AN ALLOY THEREOF, SAID SUBSTANCESPROVIDING ALL OF THE ESSENTIAL COMPONENTS OF SAID HIGH MELTING POINTCOMPOUND AND IN SUCH AMOUNT AS TO RESULT IN A SUBSTANTIAL INCREASE INTHE MELTING POINT OF THE MASS WHEN REACTION BETWEEN COMPONENTS INDIFFERENT ONES OF SAID SUBSTANCES OCCURS, SAID SUBSTANCES BEING SOCOMPOSED INDIVIDUALLY THAT EACH CONTAINS NO MORE THAN A RELATIVELY SMALLAMOUNT OF ALL OF SAID COMPONENTS; THE ENERGY RELEASED FROM A CHEMICALREACTION CAUSING FORMATION OF SAID COMPOUND BY CHEMICAL REACTION OFCOMPONENTS IN SAID SUBSTANCES BEING SUCH IN RELATION TO THE AMOUNTS ANDHEAT CAPACITY OF MATERIALS PRESENT AS TO RAISE THE TEMPERATURE OF THESYSTEM TO A TEMPERATURE NOT EXCEEDING THE MELTING POINT OF THE MATRIXMETAL; AND MAINTAINING THE TEMPERATURE OF SAID ADMIXTURE SUBSTANTIALLYLESS THAN THE MELTING POINT OF SAID MATRIX METAL UNTIL SOLIDIFICATION OFSAID MASS OCCURS.